Most people tend to think of image stabilization as being mainly for telephoto lenses. While it's true that their longer focal lengths tend to magnify the effects of camera shake, image stabilization can provde a very useful assist at wider angle focal lengths as well; anyone who's ever tried to blur the image of a waterfall, while keeping the surrounding landsape tack-sharp knows exactly what I'm talking about.

Sigma's OS system works well on the 150mm f/2.8 OS. With the system deactivated, the ''1/focal length'' rule of thumb is a little harder on a lens that weighs over two and a half pounds, so it isn't much of a surprise that Rob's only consistently sharp images were found with the lens used at 1/500 of a second. Around 70% of the shots were keepers at the 1/125 mark. Sigma claims an improvement of four stops when using its OS system, and if you count that most people will have a hard time getting consistently sharp shots at 1/125s, I will give them the four stops, as we note consistently sharp images all the way down to 1/60s, and 70% acceptably sharp at 1/30s.

Mouse over this chart to show results with IS activated.

IS systems tend to provide more benefit to less-stable shooters than very steady ones, so most users will see the same or greater amounts of shake reduction as we measured here. You can read more about our IS test methodology here: SLRgear IS Test Methodology, v2.